Many photographers expect that if a camera has focused properly, all their photos will look sharp.
Let me dispel that idea immediately. It's not true.
Sharpness is, to a large extent, in the “eye of the beholder.” While one person may consider a photograph sharp, another person might not. Don't ask me to define sharpness, I can't. Nikonians tried, but personally I think its definition (below) is gobbledygook.
The amount of detail that can be perceived in an image. Definition of an image in terms of focus and contrast. The combination of resolution -typically measured in terms of the number of distinguishable line pairs per millimeter- and acutance -the power to resolve detail in the transition of edges.Sharpness depends on focus, but it doesn't end there. If the camera isn't properly focused when the photograph is taken, it never will be sharp, but even if it's perfectly focused, it might not be perceived as sharp.
Sharpness depends on:
- Depth of Field
- Distance from the Subject
- Image Size
- Subject Motion
- Camera Motion
- Texture of the Subject and Background
I repeat, if your photo is out of focus, it won't look sharp. You therefore need to understand that auto-focus is not without it's shortcomings. The three most important factors influencing auto-focus are: light level, subject contrast, available edges or lines on which you can focus, and camera or subject motion. You need to learn about how to positively influence your auto-focus, and if necessary switch to manual focus to achieve “sharp” focus.
Depth of Field:
Interestingly, while it may not make sense at first, according to the subject, both a shallow, or deep depth of field can make your photograph look sharp.
Depth of field refers to how far to the front or back of the lens' focus point the subject will still be in focus.
The photo of the LACMA entrance on the right has a deep depth of field, while the photo of the Lotus below, has a shallow depth of field.
For a practical method of understanding depth of field try this experiment.
In moderate to low light, look into the distance, or perhaps close-up, according to your eyes, and notice how much in focus the scene is. Then squint your eyes and notice how much sharper the scene becomes. By squinting you've effectively reduced the hole (aperture) through which you're viewing the image. That's increased the depth of field.
Generally, the smaller the aperture, the shorter the focal length of your lens, and the further away your subject is, the greater the depth of field. Subjects which are within the depth of field are in focus.
Sometimes having the background extremely sharp due to a deep depth of field, can enhance the sharp appearance of the main subject. On the other hand, having a blurry background keeps focus on the main subject, which can cause its appearance to look extremely sharp due to the comparison to the blurry background.
Distance from the Subject:
The further away from the subject (at each focal length of your lens) the less detail your camera will be able to capture, and generally the less sharp your photo will seem.
There's no doubt when you magnify a digital photograph beyond its original size it will increase in blurriness due to the interpolation the software will use to fill in the photograph. That being said, you generally look at photos which are enlarged from further and further back as they are enlarged more and more. The further away you are from the photo, the less blurry it becomes. Some software does a better job in reducing the blurriness than others as a photograph is enlarged, but it does become less sharp, the larger it is made, regardless of the software.
Generally speaking, resolution has the least effect on perceived sharpness. There are 4MP (megapixel) cameras, for example, which can produce wonderfully sharp photos. That being said, all things being equal, in manipulating your photo, higher resolutions will enable you to produce sharper photographs.
Subject Motion and Camera Motion:
I've put these two items together, as they go hand in hand. If you're photographing a moving subject you have several options to get a sharp photo of that subject. You can pan with the subject. Panning refers to the horizontal and/or vertical movement or rotation of your camera to maintain the main subject in the same relative location within your framing of the photograph, to eliminate the motion blur of the movement of your subject. You can also increase the shutter speed to “freeze” the subject's movement. We see that technique used in sports photography often. Of course, you can let the subject blur a bit to speak to the viewer that the subject is in motion.
The other side of the coin is camera motion. If your camera shakes and you can't compensate for it, your photo will be blurry. You can compensate for camera movement in two ways. You can use a high shutter speed which will negate shaking problem, or you can use a lens/camera with vibration reduction, or optical stabilization which will compensate for the movement. Of course, you can always use a tripod or monopod too, to eliminate camera motion.
Lighting can play a major role in the perception of sharpness in the photo by either hiding or revealing detail in the photograph. Lighting can either bring out texture, lines and edges, and other details in your subject, or flatten or smooth them out. High contrast lighting against low contrast lighting, plus lighting which brings out tiny shadow in your subject will help make your photograph look sharp.
Texture of the subject and background:
The more fine detail or sharp edges in your photograph the more likely your photograph will be perceived as sharp. Edges are of particular importance in producing an image which is considered sharp. In Photoshop, for example, one of the best tools is to use the “unsharp mask” which, increases the contrast in the photograph around all the edges in the image, which makes them appear to be sharper.
If you want sharp photographs, each of the above characteristics needs to be taken into account.
By the way, in post-processing, you can considerably improve photo sharpness, as long as the photograph is in focus to start.